Exodus 19:18

In Exodus: “And the whole of Mount Sinai smoked, because God had come down upon it in fire.” Also in the Acts of the Apostles: “And suddenly there was made a sound from heaven, as if a vehement blast were borne along, and it filled the whole of that place in which they were sitting. And there appeared to them cloven tongues as if of fire, which also settled upon each of them; and they were all filled with the Holy Ghost.” Also in the sacrifices, whatsoever God accounted accepted, fire descended from heaven, which consumed what was sacrificed. In Exodus: “The angel of the Lord appeared in a flame of fire from the bush.”

9. As for the sound of the voice, however, and the bodily form of a dove, and the cloven tongues which sat upon each of them, these, like the terrible wonders wrought at Sinai, and like the pillar of cloud by day and of fire by night, were produced only as symbols, and vanished when this purpose had been served. The thing which we must especially guard against in connection with them is, lest any one should believe that the nature of God, whether of the Father, or of the Son, or of the Holy Spirit, is susceptible of change or transformation. And we must not be disturbed by the fact that the sign sometimes receives the name of the thing signified, as when the Holy Spirit is said to have descended in a bodily form as a dove and abode upon Him; for in like manner the smitten rock is called Christ, because it was a symbol of Christ.

25. But now of the clouds, and voices, and lightnings, and the trumpet, and the smoke on Mount Sinai, when it was said, “And Mount Sinai was altogether on a smoke, because the Lord descended upon it in fire, and the smoke thereof ascended as the smoke of a furnace; and all the people that was in the camp trembled; and when the voice of the trumpet sounded long and waxed louder and louder, Moses spake, and God answered him by a voice.” And a little after, when the Law had been given in the ten commandments, it follows in the text, “And all the people saw the thunderings, and the lightnings, and the noise of the trumpet, and the mountain smoking.” And a little after, “And [when the people saw it,] they removed and stood afar off, and Moses drew near unto the thick darkness where God was, and the Lord said unto Moses,” etc. …

For as, when He threatens, He shows a dark cloud; as on Mount Sinai; for “Moses,” it is said, “entered into the cloud, and into the thick darkness; and as a vapor, so went up the smoke;”and the prophet said, when speaking of His threatening, “Dark water in clouds of the air;”, so here, because it was His desire not to alarm, but to teach, it is a bright cloud.

And, it says, “there was much smoke.” (See Ex. xix. 18 .) For since God is said to be fire, and appeared thus in the bush, He indicates the fire even by the smoke. And what is “the blackness and the darkness”? He again expresses its fearfulness. Thus Isaiah also says; “And the house was filled with smoke.” ( Isa. vi. 4 .) And what is the object of “the tempest”? The human race was careless. It was therefore needful that they should be aroused by these things. For no one was so dull as not to have had his thoughts raised up, when these things were done, and the Law ordained.

II. Now when I go up eagerly into the Mount, or, to use a truer expression, when I both eagerly long, and at the same time am afraid (the one through my hope and the other through my weakness) to enter within the Cloud, and hold converse with God, for so God commands; if any be an Aaron, let him go up with me, and let him stand near, being ready, if it must be so, to remain outside the Cloud. But if any be a Nadad or an Abihu, or of the Order of the Elders, let him go up indeed, but let him stand afar off, according to the value of his purification. …